1. Field of the Invention
The present general inventive concept relates to an image forming apparatus to process an image using a halftone table and a method of controlling the same.
2. Description of the Related Art
In an image forming operation using an electrophotographic method, a bitmap image which represents pixels by one bit is made by image conversion for binarizing multiple bits used for representing pixels of an image, for example, 8 bits, and a printing operation on a recording medium is performed using the bit map.
An operation for converting pixels of an image received from a host computer into a bitmap image is called a halftone process. At this time, a halftone table is generally used.
The halftone process is performed by a video controller of an image forming apparatus.
In the halftone process, printing quality may be determined depending on which halftone table is used.
Referring to FIG. 1, the existing image forming apparatus M1 includes a video controller 10, a cable 20 and a laser scanning unit (LSU) 30.
The video controller 10 temporarily stores a halftone image, which is subjected to the halftone process, in an internal memory and transmits the halftone image to the LSU 30 through the cable 20 according to a printing process.
The halftone image is transmitted through the cable 20 by one bit string in series.
The halftone table has indexes corresponding to the pixels.
As illustrated in FIG. 2A, if a gray image having a brightness of 50% is printed using the existing halftone table, shapes of dot regions A1, A2 and A3 printed on a recording medium 11 are the same. That is, as illustrated in FIG. 2B, a maximum vertical distance y 1 and a maximum horizontal distance x 1 of any dot region A1 are equal to a maximum vertical distance y2 and a maximum horizontal distance x2 of another dot region A2 adjacent thereto, respectively. Another dot region A3 also has a same shape as the dot region A1.
Referring to FIGS. 1 and 2A, if a halftone image corresponding to any horizontal line L1 of the recording medium 11 is transmitted through the cable 20, a clock signal in which a level 0 corresponding to a non-print portion and a level 1 corresponding to a print portion are repeated as illustrated in FIG. 2C is transmitted. If the clock signal in which the two levels are repeated and the repeated period is constant is transmitted, the clock signal is weak against electromagnetic interference (EMI). If the clock signal is analyzed in a frequency domain using a fast Fourier transform (FFT) algorithm, an amount of EMI may exceed the EMI standard defined in International Organization for Standardization at a specific frequency fa as illustrated in FIG. 2D.
The existing halftone table has regularity in which a predetermined pattern is repeated. When a halftone image generated on a basis of the halftone table is transmitted in series, the EMI may be excessively generated.